全文获取类型
收费全文 | 2756篇 |
免费 | 128篇 |
国内免费 | 75篇 |
专业分类
化学 | 434篇 |
晶体学 | 39篇 |
力学 | 26篇 |
综合类 | 13篇 |
数学 | 1376篇 |
物理学 | 1071篇 |
出版年
2023年 | 5篇 |
2022年 | 15篇 |
2021年 | 13篇 |
2020年 | 18篇 |
2019年 | 51篇 |
2018年 | 54篇 |
2017年 | 27篇 |
2016年 | 28篇 |
2015年 | 30篇 |
2014年 | 55篇 |
2013年 | 114篇 |
2012年 | 69篇 |
2011年 | 110篇 |
2010年 | 103篇 |
2009年 | 226篇 |
2008年 | 268篇 |
2007年 | 193篇 |
2006年 | 202篇 |
2005年 | 127篇 |
2004年 | 116篇 |
2003年 | 100篇 |
2002年 | 120篇 |
2001年 | 86篇 |
2000年 | 107篇 |
1999年 | 94篇 |
1998年 | 81篇 |
1997年 | 53篇 |
1996年 | 63篇 |
1995年 | 62篇 |
1994年 | 53篇 |
1993年 | 51篇 |
1992年 | 47篇 |
1991年 | 26篇 |
1990年 | 18篇 |
1989年 | 16篇 |
1988年 | 9篇 |
1987年 | 18篇 |
1986年 | 14篇 |
1985年 | 14篇 |
1984年 | 9篇 |
1983年 | 2篇 |
1982年 | 12篇 |
1981年 | 13篇 |
1980年 | 12篇 |
1979年 | 21篇 |
1978年 | 11篇 |
1977年 | 10篇 |
1976年 | 5篇 |
1975年 | 2篇 |
1974年 | 4篇 |
排序方式: 共有2959条查询结果,搜索用时 31 毫秒
91.
AlSiP3 is formed by heating aluminum and silicon powder with red phosphorus and adding small amounts of iodine or AlCl3. Small, black crystals with metallic lustre grow at 1200°K. The compound crystallizes in the orthorhombic space group Pmnb (No. 62) with a = 987.2 pm, b = 586.1 pm, c = 608.8 pm and four formula units. In the structure isolated P atoms as well as P2 pairs are present (PP = 218.2 pm). Silicon is tetrahedrally bonded (SiP = 224.2 ? 228.2 pm) whereas aluminum has octahedral coordination (AlP = 244.2 – 260.8 pm). The structure can be described as an intergrowth structure of wurtzite and pyrite type. 相似文献
92.
Tae -Kyu Ha 《Theoretical chemistry accounts》1977,43(4):337-349
Configuration interaction (CI) studies of ground, n *, * * electronically excited states are reported for pyridine N-oxide. The transition energy to the lowest * excited 1
B
2 state is calculated at 4.35 eV, compared to the experimental spectrum range of 3.67–4.0 eV. This state lies below the lowest n * excited 1
A
2 state calculated at 4.81 eV above the ground state. The only experimentally reported triplet state at 2.92 eV above the ground state is predicted to be the 3
A
1 (*) state. The calculated energy lies at 3.27 eV. Numerous other high-lying singlet states as well as the triplet states have also been calculated. The intramolecular charge transfer character of the ground and the excited states have been studied in terms of the calculated dipole moment and other physical properties. 相似文献
93.
Aacute;gnes Buvári-Barcza Antal Csámpai Lajos Barcza 《Journal of inclusion phenomena and macrocyclic chemistry》2002,42(3-4):209-212
Two guests reacting with cyclodextrins (CDs) may form ternary complexes, in addition to the common competition of 1:1 complexes. One of the guests can really be included into the cavity of the CD, while the second guest molecule is either inserted close to the first one or attached to the outer surface of the supramolecule by H-bonding. There is a further possibility when the included guest bears a substituent outside the cavity and the second guest can interact with it. The properties of the ternary species formed are highly influenced by the solely (or primarily) included guest. The changes are attributed to the altered properties of the hydrophilic domain of the CD. The phenomena can be proved by NMR data obtained for some binary systems of -CD inclusion complexes and acetic acid and by the stability constants of the ternary complexes formed. Allosteric effects as well as coenzyme/apoenzyme/substrate interactions could be well modelled by these types of CD complexes. 相似文献
94.
Partial molar volumes for a homologous series of amino acids and peptides have been measured in aqueous 1M sodium acetate, sodium thiocyanate, and sodium sulfate at 25°C. These data have been utilized in conjunction with the data in water to deduce partial molar volumes of transfer V
2,m
0(tr) from water to these aqueous salt solutions. The volumes of transfer for the amino acids and peptides are found to be positive. The interpretation is that this result arises from the dominant interaction of the sodium salts with the charged centers of amino acids and peptides. Thermal denaturation of the structurally homologous proteins lysozyme and -lactalbumin has been studied in the presence of these salts. Significant thermal stabilization of hen egg-white lysozyme has been observed in the presence of sodium acetate and sodium sulfate. However, the thermal stabilization observed for -lactalbumin is very small in the presence of these salts and sodium thiocyanate leads to a lowering of its thermal denaturation temperature. The rise in the surface tension of aqueous salt solutions with salt concentration has been correlated with the calorimetric and volumetric measurements. The results show that V
2,m
0(tr) depends less on the type of electrolyte than on the ionic strength of the solution. The V
2,m
0(tr) values correlate very well with the increase in the surface tension of aqueous salt solutions, indicating significant role of surface tension in interactions of amino acids, peptides, or protein with the salts. 相似文献
95.
Masatoshi Taniguchi Ken-ichi SuzumuraKoji Nagai Tomihisa KawasakiTetsu Saito Jun TakasakiKen-ichi Suzuki Shigeo FujitaShin-ichi Tsukamoto 《Tetrahedron》2003,59(25):4533-4538
The isolation and structure elucidation of YM-254890, a novel Gq/11 inhibitor from Chromobacterium sp. QS3666, is described. The gross structure was determined by one- and two-dimensional NMR studies and mass spectrometry. YM-254890 is a cyclic depsipeptide containing uncommon amino acids; β-hydroxyleucine (two residues), N,O-dimethylthreonine and N-methyldehydroalanine. YM-254890 exists as a mixture of two conformers in a variety of NMR solvents, and the distinction between major and minor conformers appears to lie in the geometry of the amide bond between 3-phenyllactic acid and N-methyldehydroalanine. The absolute stereochemistery was elucidated by Marfey's analysis and chiral HPLC analysis of the acid hydrolysate of YM-254890. 相似文献
96.
流动注射胶束化学发光法测定曲克芦丁 总被引:1,自引:0,他引:1
基于HCl介质中曲克芦丁与KIO4-MnSO4反应产生强的化学发光,且吐温-80的存在能使这一反应的化学发光强度大大增强。结合流动注射技术,建立了流动注射化学发光法测定曲克芦丁的新方法。在优化的实验条件下,曲克芦丁的质量浓度在2.0×10-7~8.0×10-5g/mL范围内与化学发光强度呈良好的线性关系,检出限为7×10-8g/mL。对1.0×10-6g/mL曲克芦丁进行11次平行测定,方法的相对标准偏差为1.8%。用于曲克芦丁片剂和针剂中曲克芦丁的测定。 相似文献
97.
Danuta M. Czakis-Sulikowska Joanna Radwańska-Doczekalska Teresa Miazek 《Monatshefte für Chemie / Chemical Monthly》1982,113(6-7):827-835
4,4-Dipyridyl and 2,2-dipyridyl complexes of rare-earth perchlorates of the formulaLn(4-dipy)8(ClO4)3HClO4 · 4H2O (Ln=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu, Y, 4-dipy=4,4-dipyridyl) andLn(2-dipy)3(ClO4)3 · 6H2O (Ln=Pr, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu, Y, 2-dipy = 2,2-dipyridyl) have been synthesized. The IR spectra of these compounds and other physical properties are discussed.
4,4-Dipyridyl- und 2,2-Dipyridylkomplexe von Seltenerdmetallperchloraten
Zusammenfassung Es wurden 4,4-Dipyridylkomplexe des TypsLn(4-dipy)8(ClO4)3HClO4 · · 4 H2O mitLn=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu, Y und 2,2-Dipyridylkomplexe des TypsLn(2-dipy)3(ClO4)3 · 6 H2O mitLn=Pr, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu und Y dargestellt. Die IR-Spektren und andere physikalische Eigenschaften werden diskutiert.相似文献
98.
P. V. Arbuzov M. G. Voronkov R. G. Mirskov V. K. Stankevich B. F. Kukharev G. R. Klimenko V. I. Rakhlin 《Russian Chemical Bulletin》1995,44(9):1755-1757
Photoinduced reactions of -vinyloxy--trialkylstannoxyalkanes, CH2=CHO(CH2)
n
OSnEt3 (n = 2 to 4), with polyhaloalkanes result in 2-perhaloalkylmethyl-substituted 1,3-dioxacyclanes.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1824–1826, September, 1995. 相似文献
99.
Summary Two -cyclodextrin (-CD)-containing polymers have been prepared either by condensation of -CD molecules with a bifunctional reagent or by grafting a -CD derivative on to a linear polymer (polyvinylimidazole). HPLC stationary phases were obtained by adsorption of the -CD polymers on to silica. The ability of these chromatographic supports to resolve racemic mixtures of organic compounds such as amino acid derivatives, phenylhydantoins, barbiturates, and hydroxycoumarin derivatives has been investigated. Results were found to depend on the chemical structure of the -CD polymers 相似文献
100.
Péter Hajnal 《Combinatorica》1991,11(2):131-143
We improve King's (n
5/4) lower bound on the randomized decision tree complexity of monotone graph properties to (n
4/3). The proof follows Yao's approach and improves it in a different direction from King's. At the heart of the proof are a duality argument combined with a new packing lemma for bipartite graphs.The paper was written while the author was a graduate student at the University of Chicago and was completed at M.I.T. The work was supported in part by NSF under GRANT number NSF 5-27561, the Air Force under Contract OSR-86-0076 and by DIMACS (Center for Discret Mathematics and Theoretical Computer Science), a National Science Foundation Science and Technology Center-NSF-STC88-09648. 相似文献